1. Field of the Invention
This invention relates to apparatus for intermittently feeding a workpiece to a press and more particularly to an arrangement for releasably connecting the drive connection between the press and the feeding apparatus to permit independent adjustments in the press and feed cycles and thereby maintain the press and feed cycles in the proper timed relation when the drive from the press is connected to the drive for the feed.
2. Description of the Prior Art
In automatic strip feeding operations, as disclosed in U.S. Pat. Nos. 3,638,846; 3,758,011; 3,784,075; 4,138,913 and 4,304,348, a continuous strip of material is fed from a coil to the dies of a press for punching, stamping, cutting or the like, of a preselected length of the material. The material must be fed from the coil in timed relation with the press operation so that when the dies contact the material, the material is released from the feed so that the feed is interrupted and the material is stationarily positioned between the dies. After the press operation is completed, the feed is actuated to advance another preselected length of the material to the press. Therefore, the feeding of the stock material to the press must be coordinated with each press operation so that prior to each operation a new segment of material is is position relative to the dies for the press operation.
U.S. Pat. No. 4,316,569 discloses an adjustable cam feed that includes an input shaft drivingly connected to a driven feed roll that is rotatably supported in a feed roll unit and is positioned in overlying relation with an idler feed roll, which is rotatably supported in the feed roll unit. The workpiece is caught between the feed rolls. The adjustable cam drive converts uniform, continuous rotation of an input shaft drivingly connected to a crankshaft of the press to non-continuous, intermittent rotation of the driven feed roll. Thus, the feed rolls intermittently advance preselected lengths of the workpiece to the press in timed relation with the press operation. Each time the press dies are actuated, another length of the workpiece is positioned between the dies.
With the above-described arrangement, a cam is nonrotatably connected to the input shaft. A cam follower rides on the cam surface of the cam and is nonrotatably connected to an output shaft associated with the driven feed roll. The cam continuously rotates with the input shaft driven by the press crankshaft and generates oscillating rotational movement of the cam follower through a preselected angular path. Upon one complete rotation of the cam, the cam follower is rotated in a first direction through an arc of a preselected angle and then is rotated in the opposite direction back through the same angle of rotation to the original starting position. At the end of each angle of rotation of the cam follower, the cam follower experiences a dwell. For example, after rotation in a first direction during the feeding of the workpiece to the press, a 30.degree. dwell time follows and then the feed executes a roll return, followed by another 30.degree. dwell period. During the dwell periods, there is no transmission of rotation from the cam to the cam follower. The dwell time is necessary for proper operation of the feed so that the sequence of events that takes place within the feed is in proper synchronization with the events taking place in the press. This is known as feed to press timing.
Feed to press timing heretobefore has been accomplished with substantial difficulty because the timing belt which connects the feed to the press had to be loosened and disengaged from the feed input shaft sprocket. With the press in proper position, such that the die sequence of events is correct, the timing belt is removed from engagement with the feed roll unit. The feed roll unit is then oriented to the proper position in the feed cycle in relation to the press cycle. This has been accomplished by rotating the input shaft into alignment with a preselected set of timing marks on the machine frame. At this location of alignment, the feed is positioned relative to the press to carry out the feeding operation and the press operation in the proper timed sequence. During the press operation, the workpiece is not being fed to the press. After the press operation and the release of the dies from the workpiece, a preselected length of the workpiece is fed to the press.
In connecting the timing belt from the press crankshaft to the feed input shaft, it is the common practice to tighten the belt on the feed input shaft with a belt tensioner. This is difficult without rotating the feed input sprocket, thereby displacing the input shaft from its required position relative to the press. If the timing belt is looped around the sprocket and engaged inadvertently when slack is withdrawn, the input sprocket will rotate. Extreme care must be exercised to engage the belt to the feed input sprocket in a manner such that when the slack is removed, the belt will become taut around the feed input sprocket without rotating the input sprocket and removing the input shaft from proper register with the position of the press.
The conventional timing belt includes sprockets having a pitch of either 1/2 or 7/8 inch. Consequently, the tooth engagement of the belt to the sprocket takes place only at increments of 1/2 or 7/8 inch. As a rule, seldom does the belt tooth properly engage the pulley tooth without requiring some degree of rotation of the feed input shaft. This has the disadvantage of removing the angular position of the feed input shaft from proper register with the press position.
Therefore, there is need in strip feeding apparatus to provide means for efficiently engaging and disengaging the drive connection of the strip feeding apparatus to a press without displacing the position of the feed input shaft from preselected register with the position of the press so that the required synchronization between the operation of the press and the operation of the feed is maintained.